Phi-OTDR sensing system, interference optical signal demodulation method and vibration detection device

Abstract

The invention relates to a phi-OTDR sensing system, an interference optical signal demodulation method and a vibration detection device, and the system employs a pulse laser source to generate a detection pulse through an acoustic optical modulator, carries out the optical power amplification through a two-stage erbium-doped optical fiber amplifier, and is provided with an optical fiber circulator between the two stages; the amplified optical signal is injected into a discrete Rayleigh scattering enhanced optical fiber, and the optical fiber is provided with a piezoelectric transducer to realize vibration simulation; a back-stage optical path constructs an unbalanced Mach-Zehnder interferometer through a 3 * 3 coupler, one path of the output end of the coupler is directly connected with a Faraday rotating mirror to serve as a first interference arm, the other path of the output end of the coupler is connected to the Faraday rotating mirror through a delay optical fiber to form a second interference arm, and three paths of 120-degree phase difference signals generated by the interferometer are received by three paths of photoelectric detectors; and the phase change is demodulated by transmitting the signal to the PC terminal through the oscilloscope. According to the invention, interference signals can be demodulated, interference optical signals and noise signals are separated, monitoring of micro-disturbance and low-frequency vibration is realized, and system misinformation is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber communication technology, in particular to a φ-OTDR sensing system, an interference optical signal demodulation method and a vibration detection device. BACKGROUND

[0002] In the 1970s, optical fiber sensing technology has developed rapidly with the progress of optical fiber communication technology. With the development of technology, different kinds of sensing technology have gradually emerged. Among various optical fiber sensing technologies, distributed optical fiber sensing technology is a research direction that is currently very concerned at home and abroad. Distributed optical fiber sensing technology uses the one-dimensional spatial continuity of optical fiber for sensing. Optical fiber can be used as both a sensing element and a transmission element, integrating transmission and sensing functions. It can continuously measure the environmental parameters along the optical fiber direction and obtain the spatial distribution state and time-varying information of the measured quantity, realizing long-distance sensing.

[0003] OTDR (Optical Time Domain Reflectometer) is born on this basis. It locates the optical fiber breakpoints or losses by analyzing the light intensity attenuation of backscattered Rayleigh light in the optical fiber, but the sensitivity is limited. φ-OTDR introduces phase information on this basis, uses coherent detection technology to capture the small changes in optical fiber refractive index or length caused by external disturbances (such as vibration and sound wave), which causes the phase of backscattered Rayleigh light to change, resulting in changes in backscattered Rayleigh interference signal to realize detection. Since the distributed optical fiber sensing based on φ-OTDR has the advantages of long distance and low cost, it has been gradually applied to various professional fields such as earthquake wave detection, pipeline leakage detection, border security, underwater detection, etc., and has broad application prospects.

[0004] Due to the principle of φ-OTDR, the scattered light is weak, and the effective signal containing vibration is easily submerged in noise due to the influence of multipath effect, so there is a detection defect for small disturbances and low-frequency vibration. In actual application, the phenomenon of missing report or false report often occurs. SUMMARY

[0005] Therefore, the present application aims to provide a φ-OTDR sensing system, an interference optical signal demodulation method and a vibration detection device that can demodulate and separate the phase of the effective signal containing vibration and the noise signal, and realize detection of small disturbances and low-frequency vibration. To achieve the above-mentioned purpose, the present application provides a φ-OTDR sensing system in the first aspect, which comprises: laser source, acousto-optic modulator, first erbium-doped fiber amplifier, first fiber circulator, discrete Rayleigh scattering enhanced fiber, piezoelectric transducer, second erbium-doped fiber amplifier, second fiber circulator, 3×3 coupler, delay fiber, first Faraday rotator mirror, second Faraday rotator mirror, 3×3 demodulator; The discrete Rayleigh scattering enhanced fiber is provided with three enhanced discrete Rayleigh scattering points, and the spacing between adjacent scattering points is L; the 3×3 coupler is a non-balanced Mach-Zehnder interferometer; the laser source is connected to the input end of the acousto-optic modulator, the output end of the acousto-optic modulator is connected to the input end of the first erbium-doped fiber amplifier, the output end of the first erbium-doped fiber amplifier is connected to port one of the first fiber circulator, port two of the first fiber circulator is connected to the discrete Rayleigh scattering enhanced fiber, the piezoelectric transducer acts on the analog vibration signal of the discrete Rayleigh scattering enhanced fiber, and port three of the first fiber circulator is connected to the input end of the second erbium-doped fiber amplifier; the output end of the second erbium-doped fiber amplifier is connected to port one of the second fiber circulator. The interference optical path of the sensing system comprises two interference arms, port two of the second fiber circulator is connected to port one of the 3×3 coupler, port three of the second fiber circulator is connected to the 3×3 demodulator, port four of the 3×3 coupler is connected to the first Faraday rotator mirror and is provided with a delay fiber with a length of L / 2 therebetween, constituting a first interference arm, and the scattering light of the enhanced Rayleigh scattering point one passes through the first interference arm. Port three of the 3×3 coupler is connected to the 3×3 demodulator, port six of the 3×3 coupler is connected to the second Faraday rotator mirror and is free of a delay fiber therebetween, constituting a second interference arm, and the scattering light of the enhanced Rayleigh scattering point two passes through the second interference arm. Port one, two and three of the 3×3 coupler correspond to port four, five and six respectively, and the 3×3 coupler causes the three output optical signals to have a phase difference of 120° therebetween and enter the 3×3 demodulator respectively.

[0006] Preferably, the discrete Rayleigh scattering enhanced fiber forms defects at discrete points by ultraviolet irradiation of a hydrogen-loaded optical fiber, so that the local Rayleigh scattering intensity is higher than that of other regions of the optical fiber, forming enhanced discrete Rayleigh scattering points.

[0007] Preferably, the 3×3 demodulator comprises a PC, an oscilloscope and first, second and third photodetectors for demodulating three-phase 120° interference signals, and the first, second and third photodetectors are connected to port three of the second fiber circulator, port two of the 3×3 coupler and port three of the 3×3 coupler respectively.

[0008] Preferably, the interference optical path satisfies: The optical path of the first interference arm is longer than that of the second interference arm by L, so that the scattering light from adjacent enhanced discrete Rayleigh scattering points interferes at the 3×3 coupler.

[0009] Preferably, the length of the delay fiber is designed to satisfy the condition that the optical path difference of the two interference arms is equal to the spacing L of adjacent discrete scattering points in the sensing fiber.

[0010] Preferably, the optical intensity expression of the three-path interference signal output by the 3x3 coupler is:

[0011]

[0012]

[0013] = +

[0014] wherein A and B are constants related to the coupler, is the phase difference of the vibration interference light signal, is the phase of the original interference light signal, is the phase of the noise.

[0015] Preferably, the first Faraday rotating mirror and the second Faraday rotating mirror are used to keep the incident light and the reflected light orthogonal, and to suppress polarization fading.

[0016] To achieve the purpose of the application, the second aspect of the present application provides an interference light signal demodulation method based on a 3x3 coupler, applied to the φ-OTDR sensing system described in the above technical solution, and the method comprises the following steps: calculating the average value of the optical intensity of the three-path interference light signal to eliminate the direct current component; differencing the three-path interference light signal after eliminating the direct current component and cross-multiplying to obtain a linear expression about the three-path interference light signal; adding the linear expression about the three-path interference light signal, integrating the addition result, and extracting the interference light signal phase and the noise phase after scaling the output to obtain the demodulation result.

[0017] To achieve the purpose of the application, the third aspect of the present application provides a φ-OTDR vibration detection device, comprising: a φ-OTDR sensing system described in the above technical solution; a piezoelectric transducer acting on the discrete Rayleigh scattering enhanced optical fiber of the sensing system to simulate a vibration signal; a data processing module provided in the PC of the 3x3 demodulator of the sensing system, used to demodulate the phase of the three-path interference light signal and output a data processing result; a vibration monitoring and prompting module used to monitor and prompt the vibration according to the data processing result of the data processing module.

[0018] Preferably, the data processing module performs the following steps to demodulate the phase of the three-path interference optical signal: Calculate the average value of the three-path interference optical signal light intensity to eliminate the direct current component; Differential and cross-multiply the three-path interference optical signal after eliminating the direct current component to obtain a linear expression about the three-path interference optical signal; Add the linear expression about the three-path interference optical signal, and extract the phase of the separated interference optical signal and the noise phase after integrating the addition result and scaling the output to obtain the demodulation result.

[0019] Compared with the prior art, the present application has the following beneficial effects: The present application enhances the Rayleigh scattering signal by using discrete Rayleigh scattering enhanced optical fiber, realizes interference by using a delay optical fiber, connects a 3*3 coupler with a Faraday rotating mirror, and sets the distance between adjacent discrete enhanced Rayleigh scattering points and the distance of the delay optical fiber to make the enhanced scattering signal realize interference at the 3*3 coupler, demodulate the interference signal, separate the interference optical signal and the noise signal, realize the monitoring of small perturbations and low-frequency vibrations, and reduce system false alarms. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall structure of a φ-OTDR sensing system in one embodiment. Figure 2 It is a step flow chart of an interference optical signal demodulation method based on a 3*3 coupler in one embodiment.

[0021] 1-laser source, 2-acoustooptic modulator, 3-first erbium-doped fiber amplifier, 4-first fiber ring, 5-discrete Rayleigh scattering enhanced optical fiber, 6-piezoelectric transducer, 7-second erbium-doped fiber amplifier, 8-second fiber ring, 9-3*3 coupler, 10-delay optical fiber, 11-first Faraday rotating mirror, 12-second Faraday rotating mirror, 13-3*3 demodulator, 14-first photodetector, 15-second photodetector, 16-third photodetector, 17-oscilloscope, 18-PC, 19-discrete enhanced Rayleigh scattering point one, 20-discrete enhanced Rayleigh scattering point two, 21-discrete enhanced Rayleigh scattering point three. DETAILED DESCRIPTION

[0022] In order to make the purposes, technical solutions and advantages of the present application clearer, the following further describes the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. The following embodiments are used to illustrate the present application, but do not limit the scope of the present application.

[0023] In the description of this invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] Example 1 Embodiment 1 of this application provides a φ-OTDR sensing system, such as Figure 1 As shown, the system includes: 1. Laser source; 2. Acousto-optic modulator; 3. First erbium-doped fiber amplifier; 4. First fiber circulator; 5. Discrete Rayleigh scattering enhanced fiber; 6. Piezoelectric transducer; 7. Second erbium-doped fiber amplifier; 8. Second fiber circulator; 9. 3×3 coupler; 10. Delay fiber; 11. First Faraday rotator; 12. Second Faraday rotator; 13. 3×3 demodulator. The discrete Rayleigh scattering enhanced fiber has three enhanced discrete Rayleigh scattering points 9, 20, and 21, with a spacing of L between adjacent scattering points; the 3×3 coupler is an unbalanced Mach-Zehnder interferometer; the laser source is connected to the input of the acousto-optic modulator, the output of the acousto-optic modulator is connected to the input of the first erbium-doped fiber amplifier, the output of the first erbium-doped fiber amplifier is connected to port one of the first fiber circulator, port two of the first fiber circulator is connected to the discrete Rayleigh scattering enhanced fiber, the piezoelectric transducer acts on the discrete Rayleigh scattering enhanced fiber to simulate a vibration signal, port three of the first fiber circulator is connected to the input of the second erbium-doped fiber amplifier, and the output of the second erbium-doped fiber amplifier is connected to port one of the second fiber circulator; The interference optical path of the sensing system includes two interference arms. Port 2 of the second fiber optic circulator is connected to port 1 of the 3×3 coupler, port 3 of the second fiber optic circulator is connected to the 3×3 demodulator, and port 4 of the 3×3 coupler is connected to the first Faraday rotating mirror with a delay fiber of length L / 2 between them, forming the first interference arm, which enhances the scattered light of Rayleigh scattering point 19 through the first interference arm. Port three of the 3×3 coupler is connected to the 3×3 demodulator, and port six of the 3×3 coupler is connected to the second Faraday rotating mirror with no delay fiber between them, forming the second interference arm to enhance the scattered light from Rayleigh scattering point 20 through the second interference arm. Ports one, two, and three of the 3×3 coupler correspond to ports four, five, and six, respectively. The 3×3 coupler ensures that the three output optical signals have a 120° phase difference and enter the 3×3 demodulator respectively.

[0025] Preferably, the discrete Rayleigh scattering enhanced fiber forms defects at discrete points by irradiating the hydrogen-loaded fiber with ultraviolet light, so that the local Rayleigh scattering intensity is higher than that in other areas of the fiber, forming enhanced discrete Rayleigh scattering points.

[0026] Preferably, the 3x3 demodulator includes a PC-18, an oscilloscope 17, and first, second, and third photodetectors 14, 15, and 16 for demodulating the three-phase interference signals with a phase difference of 120°, the first, second, and third photodetectors being connected to port three of the second fiber circulator, port two of the 3x3 coupler, and port three of the 3x3 coupler, respectively.

[0027] Preferably, the interference optical path satisfies: The optical path of the first interference arm is longer than that of the second interference arm by L, so that the scattered light from adjacent enhanced discrete Rayleigh scattering points interferes at the 3x3 coupler.

[0028] Preferably, the length of the delay fiber is designed to satisfy the condition that the optical path difference between the two interference arms is equal to the distance L between adjacent discrete scattering points in the sensing fiber.

[0029] Preferably, the light intensity expression of the three interference signals output by the 3x3 coupler is:

[0030]

[0031]

[0032] = +

[0033] where A and B are constants related to the coupler, is the phase difference of the vibrated interference light signal, is the phase of the original interference light signal, is the phase of the noise.

[0034] Preferably, the first and second Faraday rotator mirrors are used to keep the incident light and the reflected light orthogonal, suppressing polarization fading.

[0035] When the laser source output light passes through the acousto-optic modulator and the erbium-doped fiber amplifier for amplification, the modulated light enters the sensing fiber. The sensing fiber uses a discrete Rayleigh scattering enhanced fiber, which is prepared by irradiating the hydrogen-loaded fiber with ultraviolet light to enhance the defects in the sensing fiber at this point, achieving the effect of enhancing Rayleigh scattering, which is stronger than the scattered light in other places of the sensing fiber and easier to detect. The distance between the two discrete enhanced Rayleigh scattering points in the fiber sensing fiber is .

[0036] When the vibration is contacted, the refractive index of the optical fiber at the vibration changes due to the influence of the photoelastic effect, which ultimately causes the scattered light to be affected, resulting in a change in the phase of the scattered light at that point.

[0037] Photoelastic effect, also known as photoelastic effect or pressurization effect, refers to the phenomenon that the refractive index of the medium changes when it is subjected to mechanical stress. Initially, it refers to the anisotropic medium in optics, which becomes birefringent.

[0038] Let the principal refractive index of uniaxial crystal be . The refractive index of light vibrating in the direction of stress, the principal refractive index . The refractive index of light vibrating perpendicular to the stress direction, at this time the photoelastic effect is related to the stress The relationship can be expressed as

[0039] In the formula, is a material constant, is the birefringence, which represents the size of birefringence, and also represents the strength of the photoelastic effect. If the thickness of the material through which the light wave passes is , the optical path difference obtained is

[0040] Therefore, the corresponding phase difference is

[0041] When the scattering light of enhanced discrete Rayleigh scattering point one and the scattering light of enhanced discrete Rayleigh scattering point two pass through the circulator to the optical fiber amplifier, the scattering light is amplified. The amplified scattering light enters the coupler again through the circulator, and passes through the coupler to the two interference arms, and the incident light and the reflected light are kept orthogonal by the Faraday rotator mirror, and are not affected. At the same time, the length difference between the interference arm of the delay fiber connected with FRM1 and the interference arm of the delay fiber without FRM2 is , so that the optical path difference of the incident light and the reflected light of the two arms is . The scattering light of enhanced discrete Rayleigh scattering point one passes through an interference arm containing a delay fiber, and the scattering light of enhanced discrete Rayleigh scattering point two passes through an interference arm without a delay fiber, and finally the optical path difference is designed to interfere at the coupler, and when the two beams of light interfere, there is

[0042] Among them and are the amplitudes of the above two beams of light, and in the above process The phase difference between two coherent light beams is caused by vibration. By detecting the change in the intensity of the interference light after interference, the phase change of the two coherent signals can be determined. In this device, a 3*3 demodulator is used for demodulation. The optical signal after interference enters the 3*3 demodulator. Due to the 3*3 coupler, the three output optical signals are 120° out of phase with each other.

[0043] Let the intensity of the three output beams be I1, I2, and I3 respectively:

[0044]

[0045]

[0046] in, = + A and B are constants related to the coupler. The phase difference of the interference light signal after vibration. The phase of the original interference light signal. The phase of the noise.

[0047] Example 2 Embodiment 2 of this application, based on Embodiment 1, provides a method for demodulating interference optical signals using a 3×3 coupler, such as... Figure 2 As shown, the steps of this method include: S1: Calculate the average intensity of the three interferometric light signals to eliminate the DC component; S2: Differentiate and cross-multiply the three interferometric optical signals after eliminating the DC component to obtain a linear expression for the three interferometric optical signals; S3: Add the linear expressions for the three interferometric optical signals, integrate the sum, and calibrate the output to extract and separate the phase of the interferometric optical signal from the noise phase, thus obtaining the demodulation result.

[0048] Specifically as follows: From equations (5), (6) and (7), we can obtain

[0049] Equation (8) eliminates the DC output of the light source The influence of this, and by differentiating equations (5), (6) and (7) respectively, we can obtain

[0050]

[0051]

[0052] One of the signals that eliminates DC is multiplied by the other two differential signals, i.e.

[0053] Similarly, we can obtain

[0054]

[0055] Adding equations (12), (13) and (14) together, we get

[0056] Integrating equation (15) and then scaling the system output yields the signal. ,according to You can then obtain The phase change is used to obtain the demodulation result.

[0057] Example 3 This embodiment 3, based on embodiments 1 and 2, provides a φ-OTDR vibration detection device, including: The sensing system described in Example 1; A piezoelectric transducer is applied to a discrete Rayleigh scattering-enhanced optical fiber of the sensing system to simulate vibration signals. The data processing module, located in the PC of the 3×3 demodulator of the sensing system, is used to demodulate the phase of the three interference optical signals and output the data processing results. The vibration monitoring and alert module is used to monitor and alert on vibrations based on the data processing results from the data processing module.

[0058] The data processing module performs the following steps, namely the interference optical signal demodulation method described in Example 2, to demodulate the phase of the three interference optical signals: Calculate the average intensity of the three interferometric light signals to eliminate the DC component; Differentiate and cross-multiply the three interferometric optical signals after eliminating the DC component to obtain a linear expression for the three interferometric optical signals; The linear expressions for the three interferometric optical signals are added together, the result is integrated, and the output is calibrated. The phase of the interferometric optical signal and the noise phase are then extracted and separated to obtain the demodulation result.

[0059] In summary, the present application provides a kind of φ-OTDR sensing system, interference optical signal demodulation method and vibration detection device, by using discrete Rayleigh scattering enhanced optical fiber enhances Rayleigh scattering signal, by delay optical fiber to realize interference, using 3×3 coupler is connected with Faraday rotator mirror and by setting the distance of adjacent discrete enhanced Rayleigh scattering point and the distance of delay optical fiber makes that enhanced scattering signal realizes interference at 3×3 coupler, and interference signal is demodulated, separates interference optical signal and noise signal, realizes the monitoring of small disturbance and low frequency vibration, reduces system false alarm, compared with prior art, the optical path structure of the present application is simpler.

Claims

1. A φ-OTDR sensing system, characterized in that, It comprises: a laser source, an acousto-optic modulator, a first erbium-doped fiber amplifier, a first fiber circulator, a discrete Rayleigh scattering enhanced fiber, a piezoelectric transducer, a second erbium-doped fiber amplifier, a second fiber circulator, a 3x3 coupler, a delay fiber, a first Faraday rotator mirror, a second Faraday rotator mirror, a 3x3 demodulator; The discrete Rayleigh scattering enhanced fiber is provided with three enhanced discrete Rayleigh scattering points, and the spacing between adjacent scattering points is L; the 3x3 coupler is a non-balanced Mach-Zehnder interferometer; the laser source is connected to the input end of the acousto-optic modulator, the output end of the acousto-optic modulator is connected to the input end of the first erbium-doped fiber amplifier, the output end of the first erbium-doped fiber amplifier is connected to port one of the first fiber circulator, port two of the first fiber circulator is connected to the discrete Rayleigh scattering enhanced fiber, the piezoelectric transducer acts on the discrete Rayleigh scattering enhanced fiber to simulate a vibration signal, port three of the first fiber circulator is connected to the input end of the second erbium-doped fiber amplifier, and the output end of the second erbium-doped fiber amplifier is connected to port one of the second fiber circulator; The interference optical path of the sensing system comprises two interference arms, port two of the second fiber circulator is connected to port one of the 3x3 coupler, port three of the second fiber circulator is connected to the 3x3 demodulator, port four of the 3x3 coupler is connected to the first Faraday rotator mirror and is provided with a delay fiber with a length of L / 2 therebetween, forming a first interference arm, and the scattering light of the enhanced Rayleigh scattering point one passes through the first interference arm; Port three of the 3x3 coupler is connected to the 3x3 demodulator, port six of the 3x3 coupler is connected to the second Faraday rotator mirror and is not provided with a delay fiber therebetween, forming a second interference arm, and the scattering light of the enhanced Rayleigh scattering point two passes through the second interference arm; Port one, two and three of the 3x3 coupler correspond to port four, five and six respectively, and the 3x3 coupler makes the output 3-path optical signals mutually have a phase difference of 120° and enter the 3x3 demodulator respectively.

2. The system of claim 1, wherein, The discrete Rayleigh scattering enhanced fiber forms defects at discrete points by ultraviolet irradiation of a hydrogen-loaded optical fiber, so that the local Rayleigh scattering intensity is higher than that of other areas of the optical fiber, forming enhanced discrete Rayleigh scattering points.

3. The system of claim 1, wherein, The 3x3 demodulator comprises a PC, an oscilloscope, and first, second and third photodetectors, which are used to demodulate three-path interference signals with a phase difference of 120°, and the first, second and third photodetectors are connected to port three of the second fiber circulator, port two of the 3x3 coupler and port three of the 3x3 coupler respectively.

4. The system of claim 1, wherein, The interference optical path satisfies: The optical path of the first interference arm is longer than that of the second interference arm by L, so that the scattering light from adjacent enhanced discrete Rayleigh scattering points interferes at the 3x3 coupler.

5. The system of claim 1, wherein, The length of the delay fiber is designed to satisfy the condition that the optical path difference between the two interference arms is equal to the spacing L of the adjacent discrete scattering points in the sensing fiber.

6. The system of claim 1, wherein, The optical intensity expression of the three-path interference signals output by the 3x3 coupler is: = + where A and B are constants related to the coupler, is the phase difference of the vibrated interference light signal, is the phase of the original interference light signal, is the phase of the noise.

7. The system of claim 1, wherein, The first Faraday rotator mirror and the second Faraday rotator mirror are used to make the incident light and the reflected light orthogonal, and to suppress polarization fading.

8. A method for demodulating an interferometric optical signal based on a 3x3 coupler, applied to the system of any of claims 1-7, characterized in that, The method comprises the following steps: Calculate the average value of the optical intensity of the three-path interference optical signals to eliminate the direct current component; The three-path interference optical signals after removing the direct current components are differentiated and cross-multiplied to obtain a linear expression about the three-path interference optical signals; The linear expressions about the three-path interference optical signals are added, and the added result is integrated and scaled to extract the interference optical signal phase and the noise phase to obtain a demodulation result.

9. A φ-OTDR vibration detection apparatus, characterized by comprising: The sensing system according to any one of claims 1-7; a piezoelectric transducer acting on the discrete Rayleigh scattering enhanced optical fiber of the sensing system to simulate a vibration signal; a data processing module arranged in a PC of a 3*3 demodulator of the sensing system, used to demodulate the phase of the three-path interference optical signals and output a data processing result; a vibration monitoring and prompting module used to monitor and prompt the vibration according to the data processing result of the data processing module. The data processing module performs the following steps to demodulate the phase of the three-path interference optical signals:

10. The apparatus of claim 9, wherein, calculating the average value of the light intensity of the three-path interference optical signals to remove the direct current components; differentiating the three-path interference optical signals after removing the direct current components and cross-multiplying to obtain a linear expression about the three-path interference optical signals; adding the linear expressions about the three-path interference optical signals, and integrating and scaling the added result to extract the interference optical signal phase and the noise phase to obtain a demodulation result. ​

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